Recently, for the diagnosis and prophylaxis of diabetes mellitus, the importance of periodically monitoring blood glucose levels has been increasingly emphasized. Currently, strip-type biosensors designated to be used in hand-held portable measuring devices allows individuals to readily monitor glucose levels in the blood.
Many various commercially available biosensors measure the blood glucose content of blood samples using an electrochemical technique. The principle of the electrochemical technique is based on the following Reaction 1.Glucose+GOx-FAD→Gluconic acid+GOx-FADH2 GOx-FADH2+electron transfer mediator (oxidation state)→GOx-FAD+electron transfer mediator (reduction state)  <Reaction 1>
In Reaction 1, GOx represents glucose oxidase, GOx-FAD and GOx-FADH2 respectively represent an oxidized and a reduced state of glucose-associated FAD (flavin adenine dinucleotide), a cofactor required for the catalysis of glucose oxide.
For electron transfer mediators, the electrochemical biosensor uses organic electron transfer materials such as ferrocene, or ferrocene derivatives, quinones, quinone derivatives, organic or inorganic materials containing transition metals (hexamine ruthenium, polymers containing osmium, potassium ferricyanide, and the like), organic conductive salts, and viologens.
A principle of measuring the blood glucose level using the biosensor is as follows.
Glucose in the blood is oxidized to gluconic acid by the catalytic activity of glucose oxidase. In this case, the cofactor FAD of the glucose oxidase is reduced to FADH2. The reduced FADH2 transfers electron to the mediator, so that FADH2 returns to its oxidized state and the mediator is reduced. The reduced mediator is diffused to the surface of the electrodes, and the concentration level of the glucose is measured by using a current generated by applying an oxidation potential of the electron transfer mediator in the reduced state in the surface of the working electrode. Compared to biosensors based on colorimetry, electrochemical biosensors have the advantages of not being influenced by oxygen and allowing the use of samples, even cloudy ones, without pretreatment thereof.
Although this electrochemical biosensor is generally convenient when used to monitor and control the amount of blood glucose, accuracy of the biosensor is greatly dependent on variation between respective mass-produced lots in which the biosensors are produced. In order to eliminate such variation, most of the commercialized biosensors are designed such that a user directly inputs calibration curve information that is predetermined at the factory into a measuring device that is capable of reading the biosensor. However, this method inconveniences the user, and leads to inaccurate results by allowing the user to make input errors.
In order to solve this problem, a method by which the resistance of each electrode can be adjusted such that production information for each lot is stored at the location at which contact of the electrode of a sensor occurs (US20060144704A1), a method in which a connection to a resistor bank is made (WO2007011569A2), and a method by which information is read by varying resistance through the adjustment of the length or the thickness of each electrode (US20050279647A1) have been proposed. The methods proposed for the electrochemical biosensors are all based on a technique for reading electrical variation. In addition, a method for distinguishing production lot information by reading the resistivity of a conductor marked on a strip using an electrical method (U.S. Pat. No. 4,714,874) has been proposed.
However, the above-proposed methods function to accurately adjust resistance, and require a process of mass-producing the sensors first, measuring the statistical characteristics of the sensors, and post-processing the measured information again using a method of adjusting the resistance marked on the sensors. Further, the process of accurately adjusting the resistance through the post-processing, when it is marked in large quantities, is very inconvenient and is difficult to use in practical application.
Methods in which colored marks are used with a spectral system that is capable of discriminating colors to realize a colorimetric method (U.S. Pat. No. 3,907,503, U.S. Pat. No. 5,597,532, U.S. Pat. No. 6,168,957), and methods that are capable of reading bar codes (EP00075223B1, WO02088739A1) have been proposed. These methods using color or bar codes are favorable for a colorimetric method-based sensor using the spectrum system, but they have technical and economic difficulties when applied to a system using an electrochemical measurement mechanism. For example, the size and structure of the area where the electrochemical sensor strip is inserted into the measuring device for the purpose of electrical connection, that is, the connection space of the sensor strip, is very limited when constructing a device and circuit for spectroscopically identifying a structure into which the production lot information is input, which results in a great increase in system construction expense.
In addition, instead of the methods of marking the production lot information on the sensor strip, a method of recording information on a container or pack containing a sensor and allowing the information to be read by the measuring device has been proposed. However, this method also has a possibility of allowing the user to make an error.
For conventional methods developed in order for users to measure the blood glucose levels thereof using disposable electrochemical biosensor strips without the need to manually input accurate calibration curve information about biosensors, which differ from one production lot to another, into a measuring device, the sensors require a long period of time for the preparation thereof, and also require post-processing in which errors are likely to be made.
Also, conventional devices for reading hue marks using a filter or a monochromator for the wavelength of a light source encounter spatial limitations and cause problems in the construction of small-sized systems.
Thus, there is a need for a biosensor that has a mark which is simple and can be easily marked within a short time period, such as hue marks, which are convenient to print on a small area of a biosensor, or hole marks, which can be easily prepared simultaneously when the final press process for mass production is performed, thereby allowing the biosensor to be produced on a mass scale. Also, there is a need for a biosensor that has production lot information recorded on the mark through which the production lot information can be thus inputted to an insulation plate of the biosensor, so that when the biosensor is inserted into a measuring device, the production lot information is automatically identified without a mistake being made by a user, thus enabling blood glucose to be conveniently and accurately measured and being economical.
However, when a part used for automatically encoding production lot information malfunctions, incorrect production lot information may be encoded. Therefore, if malfunction of a part for encoding production lot information is determined and malfunction of the part can be alerted, an error of relying on a biosensor measuring result that is calculated incorrectly based on incorrect encoded production lot information can be prevented. Further, a user of the biosensor measuring device can repair the biosensor measuring device or replace it with a new one. Such a function can be very helpful for a diabetes patient who needs to refer to an accurate biosensor measuring result.